Silage preparation for biogas plants

Risks during silaging of renewable raw materials

Rapid reduction of the pH value keeps the silage losses low
During the silaging process. the easily available carbohydrates are converted by lactic acid bacteria under anaerobic conditions to short-chain fatty acids. This is inevitably connected with unavoidable energy losses. A rapid reduction in the pH-value is a priority for keeping losses low. By doing this, enzymatic reactions and further energy losses caused by fermentation pests are prevented as far as possible.

Critical phase: Air contact when opening the silo
Considerable losses can occur when the silo is opened, if the silage is exposed to atmospheric oxygen. Pest organisms, particularly yeasts and moulds, which are present in every silo, set about their metabolic work. A clear sign of silage spoilage and the associated energy loss is the silage becoming warm. Energy in the form of heat, which is produced and lost during storage or cutting, is not available in the fermenter for biogas production.

Protection by acetic acid
The storage stability of a silage is dependent on its fermentation acid pattern. The protective effect of acetic acid, particularly against rapid yeast multiplication, is scientifically documented. For this reason, selected heterofermentative lactic acid bacteria are incorporated into the ensiling agent: They increase the acetic acid content of a silage!

The intended purpose must be considered
While an increased acetic acid content should be encouraged in biogas plants, an extremely high acetic acid content in silage for dairy cows reduces the feed intake and therefore, is undesirable in animal feeds. A decision must be made before harvesting regarding whether the substrate will be silaged for biogas or animal feed!

The more acetic acid added, the earlier the methane production begins
Acetic acid has an additional advantage in the methanogenic phase of the biogas formation process in that it can be directly converted to methane. An effect which makes a high acetic acid level in the biogas silage even more desirable.

The effect of homo-/heterofermentative silage additives is scientifically proven
The University of Rostock has examined the biogas potential of various substrates in a batch test. The influence of acetic acid on methane production was demonstrated very clearly in laboratory tests: The silages treated with biogas ensiling agents gave higher amounts of methane.